| Canola, Brassica napus L., is an increasingly important crop in North Dakota and is grown on approximately 485,640 ha with a value of {dollar}136 million in 2004, representing 90% of the total canola hectares grown in the United States. The crucifer flea beetle, Phyllotreta cruciferae (Goeze), is the most destructive insect pest on canola, defoliating the seedling leaves and resulting in significant losses in seed quality and yield. Integration of cultural practices, such as planting dates, and insecticide-based strategies were investigated for their control of crucifer flea beetle in canola in the north central, northeast, and central regions of North Dakota during 2002 and 2003. The peak populations of flea beetles in the spring usually coincided with the emergence of the earlier-planted canola, resulting in greater feeding injury. Although the later-planted canola had a lower feeding injury by flea beetles, later-planted canola was at risk for yield loss due to heat stress during flower development in July. Different insecticide strategies and their economic risk analysis were determined for high and low rates of insecticide seed treatments, high and low rates of insecticide seed treatments plus a foliar insecticide applied 21 days after planting, and a foliar insecticide applied once or twice. Spring occurrence of the P. cruciferae in canola was studied at five different sites in North Dakota from 2002 to 2004. The first occurrence of P. cruciferae in the spring was observed from late April to mid-May and peak occurrence from mid-May to mid-June. Two methods, sticky yellow traps and sweep net samples, were evaluated for assessing spring populations. When air or turf soil temperature reached 10 C, the first occurrence of beetles was detected, and as temperatures warmed up to 15 C, spring P. cruciferae populations peaked. The most accurate models and degree-day bases were determined for forecasting first and peak occurrence of P. cruciferae. Different linear regression equations were evaluated for forecasting spring populations of flea beetles based on summer populations of P. cruciferae. |
